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参数资料
| 型号： | MAX1721EUT-T |
| 厂商： | Maxim Integrated Products |
| 文件页数： | 6/8页 |
| 文件大小： | 0K |
| 描述： | IC REG SWITCHED CAP INV SOT23-6 |
| 产品培训模块： | Lead (SnPb) Finish for COTS Obsolescence Mitigation Program |
| 标准包装： | 2,500 |
| 类型： | 切换式电容器（充电泵），反相 |
| 输出类型： | 可调式 |
| 输出数： | 1 |
| 输出电压： | -1.5 V ~ -5.5 V |
| 输入电压： | 1.5 V ~ 5.5 V |
| 频率 - 开关： | 60kHz ~ 200kHz |
| 电流 - 输出： | 25mA |
| 同步整流器： | 无 |
| 工作温度： | -40°C ~ 85°C |
| 安装类型： | 表面贴装 |
| 封装/外壳： | SOT-23-6 |
| 包装： | 带卷 (TR) |
| 供应商设备封装： | SOT-6 |
SOT23, Switched-Capacitor
Voltage Inverters with Shutdown
C1
f
1 μ F (10 μ F)
V+
V OUT
INPUT
1.5V to 5.5V
C3
1 μ F (10 μ F)
ON
OFF
2
5
IN
SHDN
6 3
C1+ C1-
MAX1719*
MAX1721
GND
OUT
1
R L
NEGATIVE
OUTPUT
-1 · V IN
25mA
C2
1 μ F (10 μ F)
C1 C2
Figure 3a. Switched-Capacitor Model
R L
4
R EQUIV
NOTE: ( ) CAPACITORS ARE FOR MAX1720.
V+
V OUT
*ON/OFF POLARITY OF SHDN IS REVERSED FOR MAX1719.
Figure 1. Typical Application Circuit
R EQUIV =
1
f × C1
C2
R L
IN
S1
C1
S2
Figure 3b. Equivalent Circuit
where the output impedance is roughly approximated
S3
S4
C2
by:
V OUT = -(V IN )
R OUT ?
1
( f OSC )
× C1
+ 2R SW + 4ESR C1 + ESR C2
The first term is the effective resistance of an ideal
Figure 2. Ideal Voltage Inverter
Charge-Pump Output
The MAX1719/MAX1720/MAX1721 are not voltage reg-
ulators: the charge pumps ’ output resistance is
approximately 23 ? at room temperature (with V IN =
+5V), and V OUT approaches -5V when lightly loaded.
V OUT will droop toward GND as load current increases.
The droop of the negative supply (V DROOP- ) equals the
current draw from OUT (I OUT ) times the negative con-
verter’s output resistance (R O ):
V DROOP- = I OUT x R O
The negative output voltage will be:
V OUT = -(V IN - V DROOP- )
Efficiency Considerations
The efficiency of the MAX1719/MAX1720/MAX1721 is
dominated by its quiescent supply current (I Q ) at low
output current and by its output impedance (R OUT ) at
higher output current; it is given by:
switched-capacitor circuit (Figures 3a and 3b), and
R SW is the sum of the charge pump’s internal switch
resistances (typically 8 ? to 9 ? at V IN = +5V). The typi-
cal output impedance is more accurately determined
from the Typical Operating Characteristics .
Shutdown Mode
The MAX1719/MAX1720/MAX1721 have a logic-con-
trolled shutdown input. Driving SHDN low places the
MAX1720/MAX1721 in a low-power shutdown mode.
The MAX1719’s shutdown input is inverted from that of
the MAX1720/MAX1721. Driving SHDN high places the
MAX1719 in a low-power shutdown mode. The charge-
pump switching halts, supply current is reduced to
1nA, and OUT is actively pulled to ground through a 4 ?
resistance.
Applications Information
Capacitor Selection
To maintain the lowest output resistance, use capaci-
tors with low ESR (Table 1). The charge-pump output
resistance is a function of C1 ’s and C2 ’s ESR.
? 1 ?
?
?
η?
I OUT
I OUT + I Q
?
?
I OUT × R OUT ?
V IN
Therefore, minimizing the charge-pump capacitor ’s
ESR minimizes the total output resistance. Table 2
gives suggested capacitor values for minimizing output
resistance or minimizing capacitor size.
6
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